The present invention relates to medical electrical stimulation generally, and more particularly to implantable atrial defibrillators.
Recently, there has been a renewed interest in the development of implantable atrial cardioverters and defibrillators, as the more serious consequences of persistent atrial fibrillation have come to be understood. In such devices, it is desirable to synchronize delivery of the defibrillation pulse to the ventricle to avoid triggering arrhythmias in the ventricle. This is especially so if the devices do not include the capability of performing ventricular, as well as atrial defibrillation.
A number of proposals have been set forth for controlling the timing of delivery of atrial cardioversion and defibrillation pulses. An early disclosure of an implantable atrial defibrillator, U.S. Pat. No. 3,952,750 issued to Mirowski et al., proposes simply synchronizing delivery of the atrial defibrillation pulse to a sensed R-wave. More recently, more complex systems have been proposed. For example, in PCT Patent Publication No. WO92/18198, published Oct. 29, 1992, it is proposed to sense ventricular activity at two separate locations in the ventricles, and to synchronize the delivery of atrial defibrillation pulses to the sensed ventricular depolarizations only when ventricular depolarizations are sensed at both locations within a short time interval. Alternatively, as proposed in U.S. Pat. No. 5,207,219, atrial defibrillation pulses are delivered synchronized to sensed ventricular depolarizations only when the ventricular depolarizations follow preceding ventricular depolarizations by an interval greater than a minimum V-V interval.